WASHINGTON — The IRS yesterday shockingly admitted it had unjustly targeted Tea Party and other conservative groups for extra tax scrutiny during the 2012 presidential campaign, and officials offered a meek apology for the inexcusable offense.

“That was wrong. That was absolutely incorrect, it was insensitive, and it was inappropriate,” said Lois Lerner, chief of the Internal Revenue Service’s tax- exempt division that went after the Tea Party.

“The IRS would like to apologize for that,” she offered.

Lerner blamed the potentially illegal activity on low-level IRS agents who flagged tax filings that included words “Tea Party” or “patriot” to check for misuses of tax-exempt status.

The agents even asked some groups to divulge lists of donors and members, which would usually be a violation of IRS policy.

Tea Party groups have complained about IRS harassment since last summer. The IRS did not explain why it came clean now.

The contrite admission by the IRS only infuriated Tea Party leaders and top Republican lawmakers, who demanded a wide-ranging probe into Obama administration political dirty tricks.

“We reject a simple apology that does nothing to alleviate the danger of this happening again,” fumed Jenny Beth Martin, a leader of Tea Party Patriots, the country’s largest Tea Party organization.

“I would be very surprised if a class-action lawsuit wasn’t in the works here,” he said.

Senate Republican leader Mitch McConnell of Kentucky demanded that the White House open a government-wide review to root out “political thuggery.”

“Make no mistake, an apology won’t put this issue to rest,” he said. “This kind of political thuggery has no place in our politics.”

House Speaker John Boehner (R-Ohio) said Congress will investigate and demanded to know what the Obama administration would do to hold accountable those responsible.

“Have other federal agencies used government powers to attack Americans for partisan reasons?” asked Boehner.

The White House distanced itself from the wrongdoing.

“The activity as described is inappropriate and needs to be thoroughly investigated and acted upon,” said White House spokesman Jay Carney.

He noted that an investigation by the independent Treasury inspector general for tax administration was already underway.

Rep. Darrell Issa (R-Calif.), chairman of the House Oversight and Government Affairs Committee, requested the IG investigation last year and suggested yesterday that the pending report prompted the IRS to admit the wrongdoing.

Issa vowed to “aggressively follow up on the IG report and hold responsible officials accountable for this political retaliation.”

A spokesman for the Treasury IG said that the release of the report had not been scheduled and no other details were available.